Various types of cement bags are known for transporting and storing cement in defined portions. Various bag constructions fulfill various points, wherein, depending on the field of application, cement composition, and environmental conditions, various demands can be made. Points, such as a sufficient mechanical strength, as a function of the size of the bag, a sufficient barrier against small particles (dust), so as to prevent a migration of the small components of the cement through the packaging material, sufficient barriers against moisture and/or a sufficient air permeability, so as to guarantee a pressure compensation during the filling and cooling of the cement bag, may play a role.
Depending on the specific requirements, various material concepts for bags are used for construction materials, which have different advantages and also disadvantages:
Simple bags that are made of one or more paper plies and are partially perforated so as to guarantee air permeability. This can be seen, for example, in German Patent Application Publication No. DE 36 13 749 A1. This concept has the lowest costs but also offers the difficulties of providing sufficient mechanical strength and protection from moisture. Nevertheless, the use of these materials due to the favorable price is still widespread. Also, there are further developments to enable the use of these so-called kraft papers with large bags, as can be seen in German Patent Application Publication No. DE 698 06 168.
Bags with one or more paper plies and a perforated plastic film. In comparison to the pure paper bags, this construction offers a clearly improved barrier for moisture/liquids. A corresponding bag which can be used for construction materials can be found in Austrian Patent Application Publication No. AT 413 273 B.
Bags made of woven plastic strips also exist, mostly produced from polypropylene, with a perforated plastic film as a barrier for liquids and dust. This construction offers a very high mechanical strength, resistance to water, and a high barrier function with regard to water. Therefore, these bags are frequently used in countries in which the mechanical stress is highest during transport and storage—for example, in the Arabic area. The costs for this material is, however, clearly higher, compared with the paper bags, because of the prices of polypropylene, in comparison to paper, and also the production of the woven bag. Several process steps are required, which are work-intensive, such as a production of the strip, a weaving of the strips to form a surface structure, a production of the perforated film, and a combination of the materials to form a surface structure consisting of several plies.
In International Application Publication No. WO 2005/012121, once again, one finds a cement bag that is intended to have a plastic ply and a carrier ply as a wall bonded with it, wherein the carrier ply can be a fabric and the plastic ply can be a hot-melt adhesive applied on the fabric, which is either perforated or porous. The wall should be gas-permeable and water-impermeable.
In German Patent Application No. DE 10 2004 013 469 A1, one can see a material combination of film and nonwoven, in which the nonwoven is used as the inner ply. As the outer ply, a film is used, which is air impermeable. The bag has an overlapping area of the film, in which an inner area of the film is perforated. A venting web, via which air should exit during the filling of the bag, is formed by a lateral airtight sealing of the overlapping. The outer ply itself is air- and water-impermeable outside the venting area. The bag thus formed is to be filled via a filling connection piece. The bag should be usable for cement, gypsum, cement- or gypsum-containing dry mixtures, meal, fodder, or other substances.